I was testing some trusts phalanx spells, so will post the findings here instead of a new thread.
I used the trusts Koru-moru and King of Hearts because they will always cast phalanx on the player character that summoned them.
Koru-morus Phalanx II cast on my Paladin with phalanx equip on, I was able to overwrite it with my own phalanx. This means that the enhancing magic skill koru-moru used to cast phalanx is lesser than my Paladins enhancing magic skill on my phalanx set, which currently sits at 398.
King of Hearts Phalanx II cast on my Paladin with phalanx equip on, I wasn't able to overwrite with my own phalanx, this means that King of Hearts enhancing magic skill is higher than that of my own enhancing magic skill on my phalanx set. To verify this, I let King of Hearts cast Phalanx II on me without my phalanx+ gear, and only then I was able to overwrite it with my phalanx equip set.
So it seems that koru-morus enhancing magic skill is lesser than that of king of hearts, and it also means that when you have king of hearts summoned, it's probably worth to let him cast phalanx on you while you're wearing the phalanx+ equip, for the benefit of potentially higher phalanx rating and duration. I am curious how much enhancing magic king of hearts is using, but not sure how to test it.